1. Field of the Invention
The invention is directed to an oscillating valve for a double acting operating cylinder with a reversing valve that is inserted between a pressure supply connector and two operating cylinder drive connectors and which is triggered via two logical NOT elements, wherein each element coordinates to an operating position and connects with one drive connector via a pressure conduit, the reversing valve periodically switching between the two operating positions.
2. The Prior Art
Such valves or valve units are known in many different applications where an operating cylinder, especially a pneumatic operating cylinder for example, extend and retract frequently. Such units are used in bulk facilities or similar arrangements, for example, where masses connected to operating cylinders constantly knock on chutes, lines, and such, in order to improve or ensure the flow of the material. The above-mentioned so-called oscillating valves assume the control of the operating cylinder's movements. Other applications in which similar oscillating movements occur include but are not limited to stirrers, or pumps.
Oscillating valves of the above-mentioned kind usually have 5/2 directional valves in slide valve designs in which the valve pistons are shifted under pressure inside the valve box by operating pistons. The reversal of the direction is obtained by two logical NOT elements where the negated connections are connected to the outlets on the side of the operating cylinder of the 5/2 directional valve. The supply for the operating pressure is on both sides directly via the same connector. In the case of pneumatic applications, the air drain connectors are equipped with exhaust air throttles.
During the oscillation the change of direction occurs by scanning the fluid pressure of the connectors on the sides of the operating cylinders of the valve. Since the exhaust air is choked with each working stroke of the pneumatic operating cylinder, stagnating pressure builds up at each respective connection. It remains until the piston of the operating cylinder comes to a halt. Since the exhaust air throttle and thus also the negated connector of the logic element has nearly ambient pressure, it pressurizes the operating piston of the respective side with pressure medium because of the negation. The valve slide therefore moves to the opposite side and thus initiates another oscillating cycle.
The start-up of the known arrangements of the above-mentioned kind is particularly disadvantageous. During each start-up, the operating cylinder extends and retracts uncontrollably, and the complete piston stroke is not yet reached. In this phase, the oscillating frequency also deviates substantially from that of the running operation. It is not until several strokes later that the state corresponding with continuous operation is reached. This is because the triggering of the oscillating valve has a stop valve connected in series which starts oscillating by applying pressure to the 5/2 directional valve and then stops it by interrupting the fluid stream. During non-operation the drive connectors leading to the operating cylinder usually contain no pressure and this causes both logic elements to be open at the beginning. Both operating pistons of the reversing valve thus have pressure applied to them when oscillation begins. Only because of a different area distribution of the reversing valve's operating element, the reversing valve moves to the side with the smaller area. Thus, the respective exit and the assigned logic element are pressurized simultaneously. The logic element now immediately interrupts the pressure supply of the respective operating valve. No stagnating pressure is present yet at the other exit because of the inertia of the system (power piston, wake space), which causes the operating piston of the reversing valve on this side to remain pressurized and thus move the valve piston of the reversing valve in the respective direction. The interaction causes the described uncontrolled movement of the valve piston and thus also of the operating cylinder during start-up. Only the slowly rising pressure level at the drive connectors on the side of the operating cylinder brings about controlled oscillation. In large operating cylinders and high oscillating frequencies, a controlled, periodic movement may not be reached at all. This disturbs many operations and severely limits the range of applications of such oscillating valves.
In addition to the start-up, the turn-off of known oscillating valves has proven to be problematic in some applications as well. When turning off a running oscillation, the operating cylinder stops in a position that cannot be determined and may then shift its position because the connectors are not pressurized. In many applications, however, it is desirable to reach a defined final position (operating piston either completely extended or retracted). If some cleaning on a stirrer driven by an oscillating valve needs to be performed, for example, it is first necessary to bring the operating cylinder into a position which makes the desired work possible at all. The system as described can still move, however, and will have to be fixed in position. This causes additional work here as well as with other applications.
It should also be mentioned that another disadvantage of the known arrangement is that it cannot be started up or turned off without an additional stop valve, and this causes further costs for the additional stop valve and the necessary installation.
The object of the present invention is to improve an oscillating valve of the above described kind in a way that the mentioned disadvantages of the known arrangements can be avoided, and particularly to find a simple means to having the oscillation occur in a controlled manner in the beginning and the end.